The present invention relates to a diagnosis system for a motor vehicle.
Recently, a motor vehicle is equipped with an electronic control system for controlling various components of an engine, such as fuel injectors, thereby improving driveability, exhaust gas emission, fuel consumption, and engine power. The electronic control system controls the components based on information represented by output signals from various sensors for detecting engine operating conditions. Accordingly, if malfunctions of components and sensors occur, the engine does not properly operate.
However, because of complexity of the electronic control system, it is difficult to immediately find out the trouble. Accordingly, a trouble diagnosis device, particularly a portable diagnosis device for easily checking the electronic control system should be provided as equipment in an auto shop.
Japanese Patent Application Laid-Open No. 58-12848 discloses a diagnosis system in which an exclusive checking device is provided for measuring a pulse duration of fuel injection and an engine speed, and for checking whether idling speed is normal. The checking device is provided for diagnosing only designated specific types of motor vehicles.
There are two types of portable diagnosis devices. One of the devices has a power source for operating the device provided therein, and the other device is supplied with a power from a battery mounted in the automobile through an external connecting member such as a cigaret lighter socket.
The device having the power source therein becomes large in size and heavy in weight, which causes reduction of operability. On the other hand, in use of the device supplied with power from the external power source, first connectors for the power source and second connectors for the data communication must be separately connected, which requires troublesome connecting operations.